A Comprehensive Experimental Study on Hydrogen-Manganese Redox Flow Batteries

Manganese-based (Mn 2+ /Mn 3+ ) redox flow batteries are promising candidates for large-scale energy storage due to their relatively low cost and high positive potential (+1.51 V), enabling higher cell voltage and energy density compared to other aqueous flow batteries. However, the main challenge in long-term operation is the precipitation of MnO 2 caused by Mn 3+ disproportionation, which leads to capacity fade and reduced cycle life. Previous studies have shown that the use of additives or complexing agents within the manganese electrolyte reduces the disproportionation rate. In this work, we show that experimental conditions of the flow battery also affect the disproportionation rate, and consequently, battery performance. Lowering the upper cut-off voltage enhances electrolyte stability. Furthermore, shorter rest periods between charge and discharge improve battery efficiency, while long rest periods may result in a transition from reversible to irreversible behavior of MnO 2 particles. Additionally, stable performance is observed when operating within a current density range of 50–100 mA cm −2 . Moreover, a consistent increase in capacity is observed during cycling at current densities below 50 mA cm −2 , opening new possibilities for system design and battery operation. Finally, an active species concentration of 0.5 M results in more stable performance and reduced precipitation.